1. Field of the Invention:
The present invention relates to a corrosion-resistant copper alloy which has excellent weather resistance, i.e, resistance to discoloration in the atmosphere and a long-lasting beautiful color tone close to gold, superior corrosion resistance, particularly, high resistance to corrosion by seawater, as well as high strength and excellent cold formability.
2. Description of the Related Art
In the production of marine propellers, tube sheets of heat exchangers in desalination plant, various kinds of valves, automative parts, oil-hydraulic parts, etc., a special aluminum bronze known as a corrosion-resistant copper alloy which has the following composition has heretofore been employed:
Al: 7.5 to 8.5%; PA1 Ni: 0.5 to 2%; PA1 Fe: 3 to 4%; PA1 Mn: 0.5 to 2%; and PA1 Al: 5 to 9%; PA1 Ni: 0.5 to 4%; PA1 Fe: 0.5 to 4%; PA1 Mn: 0.1 to 3%; PA1 Ti: 0.001 to 1%; PA1 Co: 0.001 to 1%; and PA1 B: 0.001 to 0.1%;
the balance consisting of Cu and unavoidable impurities (in the above-described composition and in the following description "%" denotes "percent by weight"; this special aluminum bronze will hereinafter be referred to as a "conventional copper alloy").
Although the above-described conventional copper alloy has excellent corrosion resistance, particularly, excellent resistance to corrosion by seawater, and high strength, it suffers from the following problems. In use, the prior art copper alloy is formed into a casting having a predetermined configuration which is produced by casting the molten alloy using, for example, a permanent mold, or the ingot of the copper alloy which is formed by, for example, continuous casting, is subjected to hot forging or hot rolling to form casting or wrought predetermined configuration, and this material is then softened by annealing process in which it is maintained at 600.degree. to 800.degree. C. for 1 to 2 hours. Thus, the conventional copper alloy is made available for practical use in a condition wherein a large amount of crystallized phases such as crystallized Fe and also a large amount of precipitated phases such as intermetallic compounds containing Fe as a principal component and Fe oxides are dispersed in the .alpha.-phase which defines the matrix of the alloy structure. Accordingly, the conventional copper alloy suffers from inferior weather resistance due to the crystallized phases and the precipitated phases and therefore loses its color easily in the atmosphere and cannot maintain its own beautiful color tone which is close to gold over a long period of time. For this reason, it is impossible to make use of the beautiful golden tone of this alloy for Western tableware, vessels, fittings for buildings and decorative articles. In addition, the prior art disadvantageously has inferior cold formability.